1. Field of the Invention
The present invention relates to heat sinks employed to dissipate heat away from heat generating electronic devices, and to buses which supply power to electronic devices. This combined heat sink and bus is to be employed with printed circuit boards in a partially sealed metallic enclosure to protect them from a generally hostile environment. Typically, a printed circuit board has a foil conductor which supplies power to the electronic active components mounted on the printed circuit board and another foil path at a ground or common potential. Often a printed circuit board will have multiple foil layers, each providing a plurality of conductor foils for various purposes. These foil levels are accessed by conductor structure, typically a hole, leading to appropriate foil conductors, into which leads from the various components are inserted for connection to the foil paths. Similarly, the printed circuit board may include mounting structure for physically mounting various printed board components such as a terminal strip of whatever type.
Heat sinks to dissipate heat away from the electronic active components, which generate relatively high levels of heat, have long been known in the art. An example of various heat sinks known in the art is provided in a publication of RCA, entitled "Linear Integrated Circuits and Mosfets" at page 1066 and published in October, 1982. The RCA heat sink illustrated is an integral heat sink projecting upward from a dual-in-line integrated circuit and is integral with the dual-in-line integrated circuit and a suggested hardware mounting for a T0-220 style package.
The amount of heat generated by a printed circuit board mounted electronic device continues to increase and unless the heat is dissipated away from the electronic device, the device will fail. It is believed that the traditional route of employing a chassis as a heat sink, for devices which have tabs at a common level, or providing an off board heat sink for high heat generating devices is not particularly suitable for the newer high heat generating devices which are switched at logic level voltages. At one time, it was believed that very high heat generating devices, such as SCRs should be mounted off board on separate heat sink arrangements, which may also act as buses. Although this approach does switch a very high heat generating device at close to logic levels, the resulting wiring and electro-magnetic interference among the various conductors posed considerable problems, which were, with some labor, successfully surmounted to a considerable degree. The off board heat sinks possessed a considerable advantage of being subject to the flow of cooling fluid to include air, across all their exposed surface. The flow of cooling fluid across all their surfaces considerably increased the amount of heat which could be successfully dissipated away from the active device mounted on the heat sink.
At least one published patent deals with printed circuit board mounted buses. U.S. Pat. No. 3,670,208 to Hovnanian et al for a MICROELECTRIC PACKAGE, BUS STRIP AND PRINTED CIRCUIT BASE ASSEMBLY describes board mounted strips, namely ground and voltage supply buses located on a card between each aligned row of wire lead mounting terminals such as holes. This patent describes various solutions to the shielding problems created by providing a power bus on the printed circuit board. It is not believed that the Hovnanian et al power buses provided any significant heat sinking, nor is any heat sinking effect discussed in the patent.
An operative printed circuit board has a great number of soldered electrical connections between component leads and the foil. The reliability of the board may be vastly enhanced by wave soldering these electrical connections. Further, wave soldering considerably reduces the costs involved in manufacturing. Often a fixture will be employed to secure the components to the board during the wave soldering process.
The previously proposed grounding and heat sink systems allow for considerable improvement in reducing the number of hardware mounting pieces to mount board components, and in the reduction of manufacturing time and costs. Additionally, improvements in power distribution and in the reduction of switching current transients in the circuit board are desirable. In any printed circuit board, board space is at a premium and the ability to achieve the same functions with reduced board space is also desirable. Lastly, there exists a need for better heat sinking of high heat generating devices which are preferably directly connected by their leads to the conductive foil of the boards.